1. Technical Field
The invention relates to a hand-held color measurement device with particular applicability in making measurements on curved surfaces.
2. Background Art
Hand-held color measurement devices of the type under discussion can be embodied, irrespective of the underlying measurement technology, as autonomous devices or as peripheral measurement devices for use in connection with a controlling computer which evaluates measurement data. Autonomous color measurement devices contain all the operating and display members necessary for measurement operations and also their own power supply and are in many cases also equipped with an interface for communicating with a computer, wherein both measurement data and control data can be exchanged with the computer. Color measurement devices which are configured as peripheral measurement devices do not generally have their own operating and display members and are controlled by the superordinate computer like any other peripheral computer device. For communicating with a computer, more modern color measurement devices are often for example fitted with a so-called USB (universal serial bus) interface, via which in many cases it is simultaneously also possible to supply power (from the attached computer).
Metallic paints and paints containing effect pigments are being used more and more nowadays, not only in the automobile industry. Such paints show a significant angular dependence. Paints containing aluminum flakes, for example, show a significant brightness flop. Paints containing interference effect pigments also show differences in color when the observation or illumination direction is changed. Multi-angle measurement devices have become established for measuring such paints. Measuring brilliance is a related topic, in which the measurement result is likewise angle-sensitive.
Measurement devices which can detect such properties have to be embodied to illuminate the measurement object at one or more different, exactly defined illumination directions (in relation to the normal onto the measurement object in the measurement spot) and to pick up the light reflected by the measurement object from at least one exactly defined observation direction (likewise in relation to the normal onto the measurement object in the measurement spot). The observation direction and the illumination direction can be exchanged. A measurement array comprising at least one illumination direction and a number of observation directions is common in practice.
One typical area of application for such color measurement devices is in the automobile industry and concerns gauging paints on vehicle body parts at a number of angles, in terms of their color and possibly additional aspects of their appearance.
One great difficulty within this application is that it is often necessary to measure on curved surfaces. If the measurement device is not placed exactly and reproducibly on the curved measurement surface, this results in deviations in the usually very narrow-tolerance illumination and observation directions, which in turn leads to distortions in the measurement values.
Hand-held color measurement devices are already known which are equipped with special bearing means for placing the devices on curved measurement objects. One known hand-held color measurement device has a bearing means in the form of an annular collar which surrounds the measurement opening. This bearing means, however, is only suitable for regular curved surfaces. Other hand-held color measurement devices are equipped with sensors which indicate to the user how he or she has to position the hand-held color measurement device. This bearing means is on the one hand relatively complicated and on the other hand requires the active involvement of the user.
It is then the intention of the present invention to improve a hand-held color measurement device of the generic type to the effect that it can be securely and reproducibly placed even onto curved measurement objects using very simple means, such that the predefined illumination and observation directions are exactly maintained and distortions in the measurement values thus avoided.
This object on which the invention is based is solved by the hand-held color measurement device in accordance with the invention, as characterized by the features of independent claim 1. Advantageous embodiments and developments of the hand-held color measurement device in accordance with the invention are the subject-matter of the dependent claims.